Motivate to blog are different to everyone. Some people use this blog as a hobby, while the others use blog for sharing experience in the certain field, some people maybe simply actualization of their self and many other reasons. If then some of blogger also get some money by writing review of some products or services which got through some of advertisement bureau, I feel its ok.
Unfortunately the "golden era" for blogger to get money from writing review it’s over caused by google who was degraded of Page Rank to all blog who write reviews. For example PR this blog was 4 but now is zero!
Even visitor to a blog not determined by PR but in fact advertisers want the review to their products or services are post in certain google page rank blog and only a few who has not objection review to their products or services posting in any rank blog.
Is this the real target of google to make imposable to blogger write reviews and in turn all advertisers use google services to promote their products??